1. Field of the Invention
The present invention relates generally to apparatuses with improved inlets and methods for transporting and metering particulate material, and in particular embodiments to particulate material handling devices with improved inlets for improving the flow of particulate material, wherein the device can be used to both transport and meter particulate material, of a great range of particle sizes, under both ambient conditions and against pressure.
2. Description of Related Art
A wide variety of equipment has been used to either transport or meter particulate material (such as, but not limited to, coal, other mined materials, dry food products, other dry goods handled in solid, particle form). Such transport equipment includes conveyor belts, rotary valves, lock hoppers, screw-type feeders, etc. Exemplary measurement or metering devices include weigh belts, volumetric hoppers and the like. In order to provide both transport and metering of particulate material, it was typically necessary to use or combine both types of devices into a system.
However, some of applicant's prior pump devices were provided with the capability of both transporting and metering particulate material. Examples of such prior designs include the rotary disk type pumps discussed in the following U.S. patents, each of which is assigned or licensed to the assignee of present invention and each of which is incorporated herein by reference: U.S. Pat. No. 4,516,674 (issued May 14, 1985); U.S. Pat. No. 4,988,239 (issued Jan. 29, 1991); and U.S. Pat. No. 5,051,041 (issued Sep. 24, 1991).
The present inventor has found that particulate solids moving through a pumping system may encounter various forces (e.g, undesirable components of drive forces, frictional forces or gravitational forces) at different locations and at different directions within the system. These forces may inhibit or even stop the normal flow of the particulate solids at certain regions or areas at or around the inlet. This may cause the particulates to eventually bridge across the inlet and stop the particulate flow through the inlet. To illustrate this, FIG. 1 shows a rotary disk type solids pump 10, which has a housing (not shown), an inlet 12 and an outlet 14. A transport channel 16 extends between the inlet 12 and the outlet 14. The transport channel 16 is formed between substantially opposed faces of two rotary disks (one is shown at 17, the other is not shown in the figure) movable relative to the housing between the inlet 14 and the outlet 16 towards the outlet 14 and at least one arcuate wall extending between the inlet 12 and the outlet 14.
The pump 10 tends to impart a tangential force or thrust 18 on the particulate solids 20 in the direction of rotation 22 of the disks 17. At the inlet 12, this tangential thrust 18 tends to force the particulate solids 20 against a stationary wall 24. As a result, the particulate solids 20 at the side of the stationary wall 24 create a mass of slow moving or stationary solids in a "dead region" 28 at or adjacent the inlet 12.
This dead region 28 can reduce the rate of flow of material into the pump (and, thus, reduce the pumping rate). The build-up and/or possible collapse of a mass of particles in the dead region can cause fluctuations in the rate of flow of material through the pump and can, thereby, adversely affect the metering accuracy of the system. In systems pumping against a gas or fluid pressure or against a pressure head formed of particles, it may be important to maintain an unobstructed pump inlet so that the pump remains full of particulate material at all times to act as a pressure barrier.
Moreover, with certain particulate materials, the stagnation of the particles at the dead region 28 can cause further problems. For example, when food materials are conveyed through the pump 10, the food material held for an extended period at the dead region 28 may spoil or deteriorate and present a serious health problem. As another example, certain types of materials with a relatively high moisture content, when held for an extended period in the dead region 28, tend to become pliable and gummy, and more difficult to handle. Therefore, it would be desirable to provide an apparatus for driving or pumping the particulate solids having an inlet designed to minimize or avoid the formation of a dead region 28 in which particles are slowed or stopped.
A number of factors must be considered in the design of an efficient device for transporting or metering particulate materials. For example, the amount, size and type of particulate material to be transported must be taken into consideration. The distance over which the material is to be transported and variations in the surrounding pressure during transport must also be taken into account. It would be desirable to provide a pump device which is capable of transporting and metering a wide variety of particulate materials under both ambient and pressurized conditions.
Large scale transport and/or metering of particulate material presents unique problems. A transport apparatus or system which is suitable for transporting one type of particulate material may not be suitable for transporting a different type of material. For example, Kentucky coals maintain reasonable integrity when transported through conventional devices such as screw feeders and conveyor belts. However, Western United States coals tend to be more friable and may be degraded to a significant degree during normal transfer operations. It would be desirable to provide an apparatus which is capable of transferring all types of coal (or other friable materials) with a minimum amount of degradation.
The water content of the particulate solids is another factor which must be considered when designing any transport system. Many transport devices which are suitable for transporting completely dry particles do not function properly when the moisture content of the particulate material is raised. The same is true for particulate metering devices. Conventional metering devices which are designed to measure dry particulates may not be well suited to meter moist solids. It would be desirable to provide a transport apparatus which is capable of moving and/or metering particulate solids regardless of their moisture content.
There are also many instances in which it is desirable to transport and meter particulate materials against pressure (e.g., wherein gas and/or fluid pressure at the output side of the transport system is greater than the gas and/or fluid pressure at the input side of the system). It would be desirable to provide an apparatus which is capable of pumping and metering under both ambient pressure conditions and against a pressure head caused either by entry into a pressurized environment (wherein the gas and/or fluid pressure of the environment on the output side of the apparatus is greater than such at the input side).
It is apparent from the above background that there is a present need for a solids handling or pumping device which operates as a single unit to provide simultaneous transport and metering of particulate material and which has an improved inlet capable of minimizing or avoiding the creation of a dead region in which particles are slowed or stopped.